The following Patent Document 1 discloses a webbing winding device that removes slight looseness, or so-called “slack” of a webbing belt in such a manner that a motor is operated when a distance with respect to an obstacle in front of a vehicle is less than a predetermined value, and a spool is rotated in the winding direction by a driving force of the motor so that the webbing belt fastened to a passenger's body is wound.
In the webbing winding device, a clutch is interposed between the spool and the output shaft of the motor. The clutch includes a base plate which is rotated by a transmitted driving force of the motor and a rotary disk which is rotatable relative to the base plate. When the base plate is rotated in the winding direction relative to the rotary disk, a pawl provided at the base plate is pressed by a pressing piece provided at the rotary disk to be rotated, and the pawl meshes with external teeth of an adapter which is not rotatable relative to the spool. Accordingly, a rotation force in the winding direction of the base plate rotated by the driving force of the motor is transmitted to the spool via the adapter, thereby rotating the spool in the winding direction.
Further, the webbing winding device includes a brake mechanism that is operated by the driving force of the motor. When the brake mechanism is operated by the driving force of the motor, a brake piece slides on a friction ring of the clutch so as to suppress the friction ring from being rotated in the winding direction. When the rotation of the friction ring in the winding direction is suppressed, the rotation of the rotary disk in the winding direction is suppressed. Accordingly, relative rotation occurs between the base plate that is rotated in the winding direction by the driving force of the motor and the rotary disk that is suppressed from being rotated in the winding direction, and as described above, the pawl is rotated so as to mesh with the external teeth of the adapter.    [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-42788.